Free Radicals and Other Reactive Species in Disease

Abstract

Free radicals are generated in a wide variety of chemical and biological systems, including the production of plastics,
the ageing of paints, the deterioration of foods, the combustion of fuels and in the human body. In living organisms, the
levels of free radicals and other ‘reactive species’ (such as hydrogen peroxide) are controlled by a complex web of antioxidant
defences, which minimise (but do not completely prevent) oxidative damage to biomolecules. One reason for this is that reactive
species play useful roles, for example, in cell signalling and especially in defence against pathogens. However, over the
long human lifespan, oxidative damage may contribute to diseases (e.g. cancer, cardiovascular disease, dementia) and perhaps
even to the ageing process itself. Some antioxidants come from the diet, whereas others (such as glutathione and the superoxide
dismutase enzymes) are made in vivo.

Key Concepts

Oxygen free radicals and other reactive species are made in vivo.

Some are made for useful purposes, some ‘accidentally’.

Their action is controlled by a balanced and coordinated network of antioxidant defences, whose aim is to modulate their levels
so as to allow their useful functions while minimising oxidative damage.

Many antioxidant defences are synthesised in vivo but some also come from diet.

Reactive species play key roles in the development of human diseases, including Alzheimer disease and cancers caused by chronic
inflammation.